Si-Sn-M Alloy Negative Electrode Suppressing Volume Expansion
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Solution Overview
Problem
Lithium ion secondary batteries used in vehicles face challenges with cycle durability due to the large volume expansion and contraction of silicon-based negative electrode materials, which affects the battery's lifespan and capacity.
Innovation Solution
A silicon-containing alloy with a specific composition, including a small amount of Al, is used as the negative electrode active material, featuring a microstructure with a silicide phase and an amorphous or low crystalline Si phase, which refines the silicide and enhances the eutectic structure to suppress expansion and improve durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based negative electrode material is used to achieve high capacity, then the energy density is improved, but the volume expansion and contraction during charge and discharge causes large volume change and diminishes cycle life
Solution Approach 1:
The patent uses a composite material consisting of Si-Sn-M alloy particles with a specific microstructure containing a silicide phase and an amorphous Si phase. This composite structure combines the high capacity of Si with the stability provided by Sn and the silicide phase, resolving the contradiction between high capacity and cycle life by suppressing volume change while maintaining charge and discharge capability.
Solution Approach 2:
The patent changes the physical and chemical parameters of the negative electrode material by creating a specific alloy composition (Si-Sn-M with 2≤Sn≤10 mass%, 25≤M≤35 mass%, 0.3≤Al≤3 mass%) and controlling the microstructure to have a specific phase composition. This parameter optimization allows the material to achieve both high capacity and good cycle durability by suppressing volume expansion.
2Quantity of substance
If a material to be alloyed with Li is used in the negative electrode to improve energy density, then the capacity increases, but the negative electrode is greatly expanded and shrunk at the time of charge and discharge
Solution Approach 1:
The patent creates a composite alloy material where Si (which provides high energy density) is combined with Sn and M (transition metal) in specific proportions. The resulting composite structure with silicide phase and amorphous Si phase suppresses volume expansion during Li alloying while maintaining high energy density, as the Sn and silicide phase act as structural buffers.
Solution Approach 2:
The patent creates local quality differences within the alloy particles by forming distinct phases: a silicide phase (containing M and Si) and an amorphous Si phase. The silicide phase locally suppresses volume expansion, while the amorphous Si phase provides Li alloying sites, achieving both high energy density and suppressed volume change through localized functional regions.
3Quantity of substance
If a Si negative electrode active material is used to achieve high capacity, then the theoretical capacity increases to 3600 mAh/g, but there is a trade-off relation between capacity and cycle durability
Solution Approach 1:
The patent uses a composite Si-Sn-M alloy material where the silicide phase and amorphous Si phase work together to maintain structural integrity during cycling. This composite structure enables the material to achieve high capacity (3600 mAh/g theoretical) while improving cycle durability by suppressing the phase transformation and particle collapse that normally occur in pure Si materials.
Solution Approach 2:
The patent incorporates Sn and transition metal M elements beforehand in the alloy structure to create a cushioning effect. The silicide phase formed by M and Si acts as a pre-established structural framework that cushions and suppresses volume changes during Li alloying, preventing particle collapse and maintaining cycle durability while enabling high capacity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively refines the silicide phase, increases the proportion of Si in the eutectic structure, and enhances the forming ability of the amorphous phase, leading to improved cycle durability and high capacity while minimizing phase transformation and particle collapse during charge and discharge.
Implementation Method 1
charge and discharge are performed by occlusion of lithium ions into and release of the lithium ions from the graphite crystals
Implementation Method 2
a part has a eutectic structure composed of the first phase and the second phase
Data Source
Figure 1
Figure 2~3
Figure 4A~5E
AI summary
To provide a means capable of improving the cycle durability of an electrical device such as a lithium ion secondary battery. A negative electrode active material containing a Si-containing alloy having a composition to be represented by Chemical Formula (1) : SixSnyMzAlwAa (in Chemical Formula (1) above, M is one or two or more transition metal elements, A is an unavoidable impurity, and x, y, z, w, and a represent values of percentage by mass, where y, z, and w are 2 ≤ y ≤ 10, 25 ≤ z ≤ 35, and 0.3 ≤ w ≤ 3, respectively, and x and a are remainder) is used in an electrical device.